Space-Efficient Algorithm for Integer Programming with Few Constraints

Integer linear programs $\min\{c^T x : A x = b, x \in \mathbb{Z}^n_{\ge 0}\}$, where $A \in \mathbb{Z}^{m \times n}$, $b \in \mathbb{Z}^m$, and $c \in \mathbb{Z}^n$, can be solved in pseudopolynomial time for any fixed number of constraints $m = O(1)$. More precisely, in time $(mΔ)^{O(m)} \text{poly}(I)$, where $Δ$ is the maximum absolute value of an entry in $A$ and $I$ the input size. Known algorithms rely heavily on dynamic programming, which leads to a space complexity of similar order of magnitude as the running time. In this paper, we present a polynomial space algorithm that solves integer linear programs in $(mΔ)^{O(m (\log m + \log\logΔ))} \text{poly}(I)$ time, that is, in almost the same time as previous dynamic programming algorithms.